Spread spectrum communication primarily serves two purposes, the first is to make the transmitted signal hard to detect by unauthorized receivers and the second is to prevent the communications from being jammed. The transmitted signal is normally spread by phase modulating a desired narrowband signal by use of a pseudonoise (PN) code sequence. At the receiver, the spread signal must be despread by correlating the spread signal with a local PN code which has the same pattern as the transmitted PN code. The despreading reconstructs the original narrowband signal to complete the communication channel.
Spread spectrum signals are typically despread (correlated) at some RF frequency. This technique, however, is relatively expensive and complex due to the need for costly quadraphase correlators and a large number of RF components such as 90.degree. hybrids, transformers, mixers, inductors, etc. Each of these items adds substantial bulk, as well as cost, to the building of a spread spectrum communicaton system.
In view of the above problems related to spread spectrum communications, there exists a need for a method and apparatus for despreading (correlating) a receive signal at baseband for eliminating the need for expensive and bulky hybrids, transformers, inductors, etc.